1. Field of the Invention
The present invention relates generally to a switch configuration for a keying operation, and more particularly to a key-entry switch device (hereinafter referred to as a key switch) preferably used for a keyboard incorporated as an input device in electronic equipment. The present invention also relates to a keyboard provided with a plurality of key switches.
2. Description of the Related Art
In a thinner or low-profile type keyboard, used in a portable electronic apparatus such as a notebook or palm-top personal computer, it is necessary to reduce the height of a key switch for a keying operation as well as to improve the operability and structural reliability of the key switch. The key switch usable in the low-profile keyboard typically includes a base section, a key top disposed above the base section, a pair of link members interlocked to each other to support and direct the key top in a vertical or upward-and-downward direction relative to the base section, and a switching mechanism capable of opening and closing a contact section of an electronic circuit in accordance with a vertical or upward-and-downward movement of the key top. The key top is movable substantially vertically relative to the base section, through an interlocking action of the link members, while maintaining a predetermined posture of the key top.
In the above key switch, a device configuration generally referred to as a gear-link-type, wherein a pair of link members are meshed in a gearing manner at one-end regions thereof with each other and thus assembled together in an interlockable manner, is known (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 9-190735 (JP-A-9-190735)). A switching mechanism configured from the combination of a sheet-like switch including a pair of flexible circuit boards respectively carrying contacts, constituting a contact section of an electric circuit, in a mutually facing arrangement (referred to as a membrane switch sheet, in this application), and an actuating member disposed between the key top and the membrane switch sheet and acting to close the contacts in accordance with the descending or downward motion of the key top, has also been widely used.
JP-A-9-190735 discloses two different configurations of a gear-link-type key switch, one of which includes a pair of link members showing an inverted V-shape as seen from a lateral direction (or in a side view) when a key top is located at the upper limit position of a vertical movement (hereinafter referred to as an inverted V-shaped gear link), and the other of which includes a pair of link members showing a V-shape as seen from a lateral direction (or in a side view) when a key top is located at the upper limit position of a vertical movement (hereinafter referred to as a V-shaped gear link). In the inverted V-shaped gear link, each link member is provided, at one end region thereof, with a tooth or teeth constituting a meshing mechanism and a pivot axle pivotably joined to a bearing portion formed in the key top and, at the opposite other end region thereof, with a slide portion slidably engaged with a guide portion formed in the base section. In the V-shaped gear link, each link member is provided, at one end region thereof, with a tooth or teeth constituting a meshing mechanism and a pivot axle pivotably joined to a bearing portion formed in the base section and, at the opposite other end region thereof, with a slide portion slidably engaged with a guide portion formed in the key top. In either configuration, during a vertical movement of the key top, the pair of link members rotate about the pivot axles in a mutually interlocking manner through the meshing mechanism, and respective slide portions of the link members move substantially in a horizontal direction under the guiding action of the guide portion of the base section or key top. In the key switch described in JP-A-9-190735, a base section is constituted by a support plate disposed under a membrane switch sheet and a housing disposed above the membrane switch sheet, and the guide portion or the bearing portion is formed on the upper surface of the housing.
In the key switch described in JP-A-9-190735, due to the configuration in which the guide portion or the bearing portion for receiving the slide portion or the pivot axle of the link member is formed on the upper surface of the housing disposed above the membrane switch sheet, the thickness of the housing is included in the dimension of the key switch in a height direction. In recent years, in order to meet the requirement of thinning of a keyboard in which key switches are installed, it is necessary to reduce the height of a key switch without impairing the operability thereof, and from this viewpoint, it is desirable to reduce, as far as possible, the dimension of a component, which may influence the height dimension of the key switch or, if possible, to eliminate such a component.
In a key switch having an inverted V-shape gear link configuration, bearing portions for pivotally support the pivot axles of link members are formed at positions near the center of the inner surface of a key top, so that, when, for example, external force is applied to the outer edge of the key top so as to pull the key top apart from the base section, the force acting to separate the bearing portion from the pivot axle of the link member tends to be increased due to leverage. As a result, the pivot axle may be disengaged from the bearing portion, and thereby the key top may be disassembled from the link member.
In contrast, in a key switch having a V-shaped gear link configuration, guide portions for receiving the slide portions of link members are formed at locations near the outer edge of the inner surface of a key top, so that there is an advantage that, for example, when external force is applied to the outer edge of the key top so as to pull the key top apart from the base section, the force acting to separate the guide portion from the slide portion of the link member is not significantly increased. However, as described above, the presence of the housing may hamper further reduction in height of the key switch. In addition, due to the configuration wherein, during the vertical movement of the key top, the slide portion of each link member is moved along the corresponding guide portion of the key top, a clearance formed between the slide portion and the guide portion may cause displacement or fluctuation of the key top in a direction intersecting a vertical movement direction.